Method of making cast alnico magnets



D 1 A. J. J. KOCH ET AL 2,862,287

METHOD OF MAKING CAST ALNICO MAGNETS Filed Dec. 11, 1953 IN VENTORS AD JOHA NE A OBUS KOCH EDSkED MA IA ilN ICUS LIPS KRIJN "JACOBUS DE VOS AGENT United States Patent METHOD OF MAKING CAST ALNICO MAGNETS Adolf Johannes Jacobus Koch, Eduard Maria Henricus Lips and Krijn Jacobus de Vos, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application December 11, 1953, Serial No. 397,659

Claims priority, application Netherlands December 17, 1952 2 Claims. (Cl. 29-15559) The invention relates to a method of manufacturing an iron-base, magnetically anisotropic permanent magnet from an iron-base alloy containing as principal elements Ni, Al and Co.

In the method of the present invention most of the crystals are so oriented that the [100l-direction is substantially parallel to the preferred direction of magnetization, in which direction the magnet is magnetized, the two ends of the magnet body are cooled relative to the remaining portion during the solidification, and the body is divided on the separation plane of the solidification fronts. As the solidification starts from the ends of magnets, which usually have parallel surfaces, the separation plane will be formed where the solidification fronts meet, usually at the center of the magnet body. The body may be readily divided on the separation plane for instance by tapping it lightly with a hammer to thereby crack the same. Not only does the occurrence of this separation plane allow the easy splitting of the casting but in addition each of the two portions of the split casting has a higher BH value than the unsplit initial casting.

It may be desirable to delay intentionally the withdrawal of heat from the part of the magnet body between the two ends, for example by carrying out a method as described in U. S. patent applications Nos. 397,658, now Patent No. 2,821,759, granted February 4, 1958 and 397,657, now abandoned both filed December 11, 1953, in which in the first case the cast outer edge is removed prior to the separation of the said parts and in the second case the withdrawal of heat is delayed preferably only in the proximity of the desired separation plane.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawing in which the single figure is a sectional view of a mould with the magnet body therein.

The sand mould 1 comprises a ring 2 of a material max 2,862,287 Patented Dec. 2, 1958 which exhibits exothermic combustion such as an aluminum containing thermit. The bottom and the lid are constituted by two thick metal chilling plates 3 and 4 respectively. The ring may be ignited by high-frequency means or automatically by the heat of the liquid alloy to be cast, by pouring the alloy into the opening 5. From the chilling plates inward crystals of the shape shown diagrammatically at 6 will then be produced. The two solidification fronts will meet approximately at the centre of the magnet body, to form a separation plane 7 on which the body may be readily divided into two parts.

What is claimed is:

1. A method of manufacturing a magnetically anisotropic permanent magnet consisting of an iron-base alloy containing nickel, cobalt and aluminum comprising the steps, introducing said alloy while molten into a mold to form a casting, placing chill plates in thermal contact with opposite ends of said casting to withdraw heat longitudinally and to promote columnar crystal growth in the []-direction, retarding transverse heat-loss from a portion of the casting intermediate the ends while the ends thereof are being cooled to form a separation plane coincident with the plane of minimum heat-loss, and dividing thecasting along the separation plane after coolmg.

2. A method of manufacturing a magnetically anisotropic permanent magnet consisting of an iron-base alloy containing nickel, cobalt and aluminum comprising the steps, introducing said alloy while molten into a mold to form a casting, placing chill plates in thermal contact with opposite ends of said casting to withdraw heat longitudinally and to promote columnar crystal growth in the [100l-direction, heating a portion of the casting intermediate the ends to retard transverse heat-loss from said portion while the ends are being cooled to form a separation plane coincident with the plane of minimum heatloss, and dividing the casting along the separation plane after cooling.

References Cited in the file of this patent UNITED STATES PATENTS 2,325,832 Christensen Aug. 3, 1943 2,578,407 Ebeling Dec. 11, 1951 2,705,353 Zeigler Apr. 5, 1955 FOREIGN PATENTS 7 619,991 Great Britain Mar. 17, 1949 642,608 Great Britain Sept. 6, 1950 652,022 Great Britain Apr. 11, 1951 661,727 Great Britain Nov. 28, 1951 684,522 Great Britain Dec. 17, 1952 

1. A METHOD OF MANUFACTURING A MAGNETICALLY ANISOTROPIC PERMANENT MAGNET CONSISTING OF AN IRON-BASE ALLOY CONTAINING NICKEL, COBALT AND ALUMINUM COMPRISING THE STEPS, INTRODUCING SAID ALLOY WHILE MOLTEN INTO A MOLD TO FORM A CASTING, PLACING CHILL PLATES IN THERMAL CONTACT WITH OPPOSITE ENDS OF SAID CASTING TO WITHDRAW HEAT LONGITUDINALLY AND TO PROMOTE COLUMNAR CRYSTAL GROWTH IN THE (100)-DIRECTION, RETARDING TRANSVERSE HEAT-LOSS FROM A PORTION OF THE CASTING INTERMEDIATE THE ENDS WHILE THE ENDS THEREOF ARE BEING COOLED TO FORM A SEPARATION PLANE COINCIDENT WITH THE PLANE OF MINIMUM HEAT-LOSS, AND DIVIDING THE CASTING ALONG THE SEPARATION PLANE AFTER COOLING. 